Imaging device and operating method thereof

An imaging device comprising:

• a first transistor;
• a third transistor;
• a fourth transistor;
• a fifth transistor;
• a photoelectric conversion element;
• and
• a first capacitor,
• wherein one electrode of the photoelectric conversion element is electrically connected to one of a source and a drain of the first transistor,
• wherein the other of the source and the drain of the first transistor is electrically connected to one of a source and a drain of the third transistor, a gate of the fourth transistor, and one electrode of the first capacitor,
• wherein one of a source and a drain of the fourth transistor is electrically connected to one of a source and a drain of the fifth transistor, and
• wherein the first transistor and the third transistor each comprise a first oxide semiconductor in a region where a channel is formed.

A method for operating an imaging device, comprising, in an n-th frame period where n is a natural number of two or more:

• resetting a potential of a first charge accumulation portion;
• charging the first charge accumulation portion with a potential in accordance with an output of a photoelectric conversion element and simultaneously reading imaging data in an (n−1)-th frame that is output in accordance with a potential of a second charge accumulation portion;
• resetting a potential of the second charge accumulation portion;
• transferring a potential of the first charge accumulation portion to the second charge accumulation portion;
• and
• holding a potential of the second charge accumulation portion.